You spend a lot of your training focused on heart rates, pacing, and mileage. All of which helps drive a higher VO2max, a faster lactate threshold pace, or greater running economy and glycogen efficiency (which is hard to quantify, of course). But if you are out to squeeze every minute out of your marathon PR, are you overlooking one key attribute that stares right back at you from the mirror every day?

No, I’m not talking about the mental aspects, though those are important. I’m talking about something that is easier than anything in the world to measure. It’s your body weight.

Run Faster by Weighing Less

You may well think that, as someone running high mileage, you can eat whatever you want and your weight will take care of itself. And to some extent, this is true, if your goal is simply to lose “a little weight” or roughly maintain what you presently weigh. But if you want to deliver your best marathon performance, finding and maintaining your right weight is a significant factor.

How much does it matter, and why? To answer the second question first, obviously carrying less weight around means you have to do less work (burn less calories) to hold a given pace. But additionally, even if you think in terms of VO2max, note that it is expressed as ml/kg/min (and, as a reminder, this is the volume of oxygen the body uses, per kg, in one minute at maximum effort). This means that, for a given VO2max, the more you weigh, the “thinner” the oxygen is spread, and the less effective you will run.

There is a calculator buried in a set of Runner’s Projection Utilities (more on this spreadsheet in future posts) that helps you predict your marathon time at given weights, assuming all else remains equal. In my case, I believe my weight was roughly 170 lbs. for the Akron Marathon in 2010, and around 162 lbs. at last year’s Towpath Marathon. The calculations on this sheet would suggest that 7 minutes of the 8 minute PR I achieved was strictly due to weighing less!!! In fact, considering that Akron was a hilly course and the Towpath was flat, I may well have been in better shape (or, at least, had a higher VO2max) in 2010.

Of course, “all else remains equal” is a bit of a broad caveat. Weight loss is good until the point that you begin to lose muscle and thus hurt your running economy (how efficiently you turn energy into forward progress). And taking in enough calories to meet your training needs is obviously critical.

So how do you go about defining your ideal weight? There’s no perfect formula for doing so – some target a low BMI (observing that most elite marathoners are in the 18-20 range), but this may not be realistic for your body structure. It seems the best bet is trial and error, finding the weight at which your calorie intakes are sufficient to support your training needs without gaining weight – after having lost weight initially.

Not only is it slimmer, it makes you faster. Hat tip to Adina on dailymile.

The Runner’s Diet – A Simple Approach

This can be very difficult to manage, no doubt – when you are running even 50 miles weekly, this is roughly the equivalent of requiring two extra days worth of meals needed each week. Calorie tracking applications like My Plate from Livestrong can help, if only to make you more conscious of the amount and types of calories you are taking in.

Calories in need to be less than calories out (it takes 3500 calories deficit to lose a pound) – it doesn’t really matter whether these are fat, carbohydrate, or protein calories. As a runner, your bias should be towards protein to help promote muscle repair and growth.

Don’t seek to lose more than a half-pound per week – anything more than that is likely to leave you a bit weak for key workouts.

Keep the same kind of balance you’d use if you weren’t running (ideally) – don’t make up the gap with “empty calories” like many snack items.

Use whatever strategy works for you – maybe it’s “grazing” through the day (though that has largely been discredited), or maybe it’s 3 squares a day. Again, it’s mostly about calories in minus calories used.

That’s really it – most of the other advice you’ll hear on low fat diets, or low carb diets, or running in the fat-burning zone really don’t work in the long run, if you can’t keep the calorie balance in mind. And for an extra minute of time in the marathon per pound lost, isn’t it worth doing so?

This post is so timely as I am training for my 6th half, I added 15 pounds (not happy about this), and am now 10 minutes over my half marathon time. My knees hurt with the extra weight, and speed work is a chore so with ten more weeks to go I intend to drop some of this extra weight so I can enjoy the experience and running once again. Great read!!

http://runningrecon.blogspot.com Drew

I couldn’t agree with you more on this post. I notice a difference in my running when my weight fluctuates just a few pounds. At 154 I feel sluggish and maintaining pace takes more effort. At 149 I’m light on my feet and it’s much easier. Beyond eating well all the time, about ten days before an A race I like to cut back on the calories a little. That way when it comes time to load up I’m not at the high end of my range. As you point out, it’s all about finding the strategy that works for you.

http://designedtorun.com/ Rob Savarese

Timely post Greg as most of us are still dealing with the post-holiday pounds. I can also attest to the fact that running 50-60 miles per week doesn’t lead to weight loss unless you moderate your calorie intake as well. I almost fainted when I learned that a Cold Stone milk shake is over 2000 calories! It’s just too easy to overeat if you’re not paying attention.

http://predawnrunner.com Greg Strosaker

Thanks Deanna, good luck on losing the weight, I think that having a time goal and recognizing the importance that weight can play in reaching the goal can be a good incentive. I do plan a future post on how to maintain reasonable weight between seasons; this was a huge challenge when I was injured last winter, and it really introduced me to the discipline of counting calories.

http://predawnrunner.com Greg Strosaker

Diet is definitely an individual think, which is part of why I hate the “shortcuts” or tricks that you so often read about. 90% of the equation is simply “calories in – calories out”, and it doesn’t matter how you take them in (fat versus carbs versus protein) or how you burn them (low HR work, high HR work, etc.). If we can all get that 90% right, in a way that works for us, then the rest is just cake. Wait, maybe that doesn’t sound right.

http://predawnrunner.com Greg Strosaker

Thanks Rob – if you think it is still a challenging equation for those of us “earning” an extra two days of meals per week (or more), imagine the mental shift required for those just starting an exercise regimen. I can’t tell you how many people I’ve seen at fitness centers who take in more calories in Gatorade during the time they are there than they actually burn in their workout.

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Hi, and welcome to Predawn Runner. I designed this blog to help provide tips and inspiration to those of you who already live a full life and want to make your running a bigger part of it, without having to sacrifice the other things that matter to you (except maybe some sleep). Whether you seek to continuously improve your performance and set new personal records or just run for health reasons, I hope you find information that helps make running a part of your routine.

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